A proposal to study the effects of clomiphene citrate on fertility in normal cycling women. Clomiphene is widely used to stimulate fertility. As indicated in the RFA for the Network, this treatment is applied without normative data for evaluating efficacy, often without established diagnoses and is expensive of time, psychological reserves and money. In fact, evidence indicates that clomiphene may actually impair fertility; therefore, its use for treatment may be counter-productive in marginal cases. We propose to study normal volunteers (defined as up to 7 months unprotected intercourse without pregnancy) in order to establish normative data for pregnancy rates, and to assess the effect of clomiphene treatment on the pregnancy rate. The experimental protocol is constructed upon the randomized, double-blind crossover model. Normative data will be obtained during the "drug washout" and placebo periods. This study has particular relevance for the RFA in fight of its direct applicability to the diagnosis and treatment of infertility, the common but unsubstantiated usage of clomiphene under these conditions, and the need for a study population which can best be obtained through the Cooperative Network.